Lubricating grease composition, its production and use

ABSTRACT

A lubricating grease composition of the type wherein mineral or synthetic oil is thickened to the properties of a lubricating grease with a polyurea compound as thickening agent, is provided, along with a method for preparation. The polyurea compound comprises the reaction product of an isocyanate with at least three isocyanate groups in the molecule with a long-chain, straight-chain or branched aliphatic monoamine to give extended temperature and wear properties. The process for the production of this lubricating grease composition involves dissolving the long-chain aliphatic amine or mixture of such amines in the base oil, adding thereto the isocyanate with at least three isocyanate groups, heating the mixture to a temperature of at least 160° to bring about gelling, and mechanically, finely comminuting the gel product.

This application is a continuation of application Ser. No. 668,723,filed Oct. 1, 1984, and now abandoned.

The invention concerns a lubricating grease composition based upon acomparatively large proportion of mineral or synthetic oil as base oiland of a smaller proportion of polyurea as thickening agent.

It is known so to thicken lubricating-active mineral or synthetic oilsby the addition of polyureas that they achieve the properties of alubricating grease. The polyureas used in these lubricating greases areproduced by the reaction of one or more monoamino- and/or diaminocomponents, which can be aliphatic or aromatic, with diisocyanates,which can also be aliphatic or aromatic. Typical examples herefor are tobe found in published Federal Republic of Germany Patent ApplicationsNos. 25 40 470, 26 04 342 and 26 04 343, as well as in publishedEuropean Patent Application No. 31 179. The lubricating greases soobtained are adjusted, by the addition of additives, to the speciallyintended use of the grease, whereby high pressure additives, anti-wearadditives and anti-oxidants are usually employed.

These greases have proved to be well suited for many purposes. Inparticular, they are suitable for comparatively high long-periodtemperatures of use as the lithium fats, with which admittedly mostlubricating problems can be satisfactorily solved but only up to amaximum temperature of use in the region of 135° C. With thepolyurea-containing lubricating greases, this temperature limit could beincreased into the range of 150° to 160° C.

However, for purposes of use under especially difficult conditions, thepreviously achieved long-term temperatures of use do not suffice.Therefore, a further increase would be desirable. Furthermore, in manycases, the stability of the polyurea thickening agent in the presence ofthe necessary additives, especially when it is a question of oil-solubleadditives, proves to be unsatisfactory.

The problem forming the basis of the invention is to reduce or overcomethese disadvantages of the previously known lubricating grease based onoil with polyureas as thickening agents.

According to the invention, this problem is solved by a lubricatinggrease composition based on a comparatively large proportion of mineralor synthetic oil as base oil and of a smaller proportion of a polyureacompound as thickening agent, as well as conventional additives, whichis characterised in that as polyurea it contains the reaction product ofan isocyanate with at least 3 isocyanate groups in the molecule with along-chained aliphatic monoamine. The polyureas used according to theinvention are cross-linked, high molecular products which have beenmechanically comminuted. The amine component preferably consistspreponderantly of the monoamines with 16 to 24 C-atoms but smallerproportions of monoamines with shorter chains down to 10 C-atoms canalso be present, whereby, however, an amount of 10% of the total amineis not to be exceeded. In the same way, small amounts of diamines can bepresent, whereby an amount of about 5% is not to be exceeded.

By the expression "long-chained aliphatic monoamine" are to beunderstood compounds with more than 14 C-atoms, preferably those with 16to 24 C-atoms and mixtures thereof. Longer chained monoamines areadmittedly technically also usable for the invention but, at the moment,are economically only difficult to obtain.

The monoamine can be a saturated fatty amine or one containing one ormore olefinic double bonds. There come into consideration not onlystraight-chained, branched but also cyclic aliphatic amines. Especiallypreferred in the case of singly unsaturated fatty amines are those with16 to 20 C-atoms, still more preferred an alkenylamine with 18 C-atoms(oleylamine), on the one hand, as well as, in the case of saturatedaliphatic alkylamines, those with 18 to 24 C-atoms, still morepreferably with 20 to 22 C-atoms, on the other hand. Each of thesepreferred embodimental forms of the polyurea display special propertieswith regard to the compatibility with additives.

In this regard, further below it sill be dealt with in more detail.

As isocyanate components with at least 3 isocyanate groups in themolecule, there come into question the commercially available compoundswhich are known, for example, as Desmodur types of the firm Bayer AG,Hylene types of the firm Du Pont, Mondur types of the firm Mobay Chem.Corp. or Nacconates of the firm Allied Chem. & Dye Corp. Triisocyanatesare preferred but tetraisocyanates and still higher polyisocyanates canalso be used, expediently in admixture with triisocyanates. In the scopeof the invention, in the following they are all referred to as"polyisocyanates". There can be used not only aliphatic polyisocyanates,such as, for example, Desmodur N, which contains tri-, tetra- and higherpolyisocyanates, as well as aromatic polyisocyanates, such as forexample, Desmodur R. The latter, in the case of which it is chemically aquestion of p,p',p"-triphenylmethane triisocyanate in the form of a 20%solution in methylene chloride, proves to be especially well suited inthe scope of the invention. In addition, the suitability of a specialpolyisocyanate in the scope of the invention can easily be ascertainedby simple preliminary experiments.

The lubricating grease composition according to the invention containsthe polyureas in an amount sufficient for the achievement of the desiredthickening action. In general, good results are obtained in the case ofadditions of between 3 and 45 wt.% of polyurea, referred to the baseoil. In general, the best results are obtained in the case of amountsbetween 8 and 15%.

As mentioned, as base oils there come into consideration mineral oil andsynthetic oil. Naphthalene-based base oils are preferred. However,paraffin-based base oils can also be used. In the latter case, polyureasare preferably used as thickening agents in the case of which themonoamine component is as long-chained as possible in the scope of therange taught by the invention.

In the case of synthetic base oils, all usual classes prove, inprinciple, to be suitable even when, with regard to the combination withthe polyurea resin, individual members of the groups in question givebetter results than others. Typical examples of suitable synthetic oilsare poly-alpha-olefins, glycols, esters, alkyl-benzenes and siliconeoils soluble in organic solvents.

The lubricating grease compositions according to the invention cancontain not only oil-soluble but also non-oil-soluble additives inorder, for example, to improve the high pressure properties, the wearbehaviour and the oxidation stability. These lubricant additives areknown to the expert and do not here require a detailed explanation,insofar as special aspects in connection with the various possible formsof variation of the polyurea used according to the invention are not tobe observed.

As solid additives with high pressure and/or anti-wear improvingproperties, there come into consideration, in particular, graphite andthe lubricating-active metal sulphides alone or in combination withactivity strengtheners. Amongst these, graphite and molybdenumdisulphide and their mixtures are, in turn, preferred in the scope ofthe invention. Suitable activity strenghteners are e.g. metal oxides,hydroxides, phosphates or fluorides. These non-oil-soluble additives areespecially suitable in combination with polyureas, the monoaminecomponent of which lies in the longer-chained range, thus between about18 and 24 C-atoms, preferably 20 to 22 C-atoms. However, they can finduse in the case of all polyureas to be used in the scope of theinvention. The amount of these non-oil-soluble additives lies, ingeneral, between 0.5 and 10 wt.%, referred to the total greasecomposition, an addition of 2 to 6% being especially preferred. If thestated amounts are exceeded, then one does not obtain any improvement ofthe properties which would justify the increased costs, in the case ofgoing below the limiting values, the properties aimed for are no longerobtained. Under the aspects of as good a long-lasting strength aspossible, friction properties and acceptable price, with 2 to 4%addition of non-oil-soluble additive and usually of oil-solubleanti-oxidant, especially satisfactory results are obtained.

An especial advantage of the lubricating grease composition according tothe invention consists, however, in the excellent compatibility withoil-soluble additives, especially also oil-soluble high pressure andanti-wear additives. In the case of previously known lubricating greaseswith polyurea additives as thickening agents, the highly effectiveoil-soluble high pressure and anti-wear additives prove to be unsuitablesince they led to a rapid breakdown of the polyureas which were producedwith diisocyanates. In this regard, permissible oil-soluble additivesgave only unsatisfactory properties to the lubricating greasecomposition. However, in the case of the lubricating grease compositionaccording to the invention, the especially effective oil-solubleadditives can also be used without displaying negative actions on thepolyurea components in long-term operation. In the case of theoil-soluble additives, the phosphorus- and sulphur-containing compoundsare preferred, as well as the replacement products for sulphurised spermoil which have recently become known. Especially good properties areachieved with the additive combinations known from published FederalRepublic of Germany Patent Application No. 1954452.

For these oil-soluble additives, those embodimental forms of thelubricating grease according to the invention have proved to beespecially suitable in the case of which the amine component of thepolyurea is unsaturated and lies in the lower range of the chain lengthcoming into consideration. In this connection, there is especiallypreferred an alkenylamine with 18 C-atoms, such as oleylamine.

The oil-soluble additives are, in general, used in amounts between 3 and20 wt.%, referred to the total lubricating grease composition. Anaddition between about 5 and 12 wt.% is preferred.

A further subject to the invention is a process for the production ofthe lubricating grease composition described above in detail. Thisprocess is characterised in that one dissolves a long-chained aliphaticmonoamine or a mixture of such amines in the base oil, addspolyisocyanate thereto, heats the mixture to a temperature of at least160° C. until a gelling takes place, mechanically finely comminutes thegelled product and adds thereto the additives and possibly further baseoil.

The process starts from the mineral or synthetic oil or mixture of suchoils which is to be used as base oil for the lubricating greasecomposition. If it is a question of a mixture of oils, then the processcan also only be carried out with one oil component and the further oilcomponents can first be added later. In the case of the process, it isalso possible to start from a smaller proportion of base oil than isneeded for the aimed for composition with regard to the amount ofpolyurea. The amount of oil must merely suffice in order completely todissolve the amine.

The aliphatic monoamine or mixture thereof is expediently introduced inmolten state into the base oil in order to simplify the dissolving,whereby the dissolving can be simplified by stirring and heating.Thereafter or simultaneously, a suitable amount of the selectedtriisocyanate is added thereto. In general, there are suitable amountsin the case of which 1/2 to 4 isocyanate groups are available per aminegroup. However, in special cases, these ratios can be exceeded or gonebelow.

The mixture obtained is heated until several recognisable reaction stepshave been passed through and finally a gelling occurs. The necessarytemperature depends upon the reaction components employed and additivespossibly present and, as a rule, lies above 160° C., preferably above200° C. In general, a heating above 240° C. is not necessary but can beused.

The gelled mass is subsequently mechanically comminuted, whereby theknown comminution methods and devices can be used. Expediently, the gelis finely ground in a colloid mill. Subsequently, the additives areadded, as well as possibly the remaining amount of base oil.

As amine, for the process there is preferred oleylamine or a saturatedalkylamine or alkylamine mixture with 20 to 22 C-atoms. With regard tothe preferred polyisocyanate, that stated above applies.

The lubricating grease composition according to the invention ischaracterised by an improved mechanical stability, especially incombination with oil-soluble additives, i.e. oil-soluble high pressureand anti-wear additives. Hitherto, however, satisfactory lubricatinggreases based on lubricating oil with polyurea as thickening agent withgood high pressure properties could only be obtained in the case of theuse of non-oil-soluble high pressure additives.

With regard to the achievable high pressure properties and the wearstability, the lubricating grease composition according to the inventionis even superior to the best known lithium greases and, at the sametime, permits an increase of the long-term use temperature, which in thecase of lithium greases lies in the region of 80° to 110° C. and brieflyof up to 135° C., to a long-term use temperature of 150° to 160° C., andbriefly still further upwards. This accords with a quite substantialimprovement of the life and temperature resistance. The lubricatinggrease composition according to the invention is, however, not inferiorto the best commercially available lubricating greases even in the lowertemperature range down to considerably below minus 30° C. Thus, itdisplays a combination of properties which has previously not been knownin the case of commercially available products.

For example, with the best known lithium greases, in the case ofespecially severe conditions, such as are present, for example, inhomokinetic flexible couplings and are simulated in drive shaft testbenches, 20 to 25 million rollings over at 50° C. can be achieved. Withthe lubricating grease compositions according to the invention, even attemperatures of 150° to 160° C., at least 30 million rollings over canbe achieved.

FIGS. 1-5 show the results produced by using the greases of theinvention.

The improved properties achieved according to the invention can be seenfrom FIG. 1 of the accompanying drawing.

FIG. 1 shows a test sheet which has been obtained with the lubricatinggrease composition of Example 1 according to the invention on thecommercially available lubricating agent test apparatus SRV availablefrom the Applicants, which is described in an "antriebstechnik", 19(1980), No. 1-2. The lubricating agent composition was, in the case ofthe given operating conditions, subjected to a loading increasing from50 to 1000 Newton, without the lubricating effectiveness therebyfailing. This means that the flow limit of the metal is reached in thesurface roughnesses without the lubricating action of the lubricatinggrease composition according to the invention being lost.

The following Examples further explain the invention.

EXAMPLE 1

4000 g. of naphthene-based base oil of 100 Centistoke at 40° C.,viscosity index about 45, are mixed with 400 g. of saturated monofattyamine with 20 to 22 C-atoms in a molten state and mixed with 1200 g. ofa 20% solution of p,p',p"-triphenylmethane triisocyanate in methylenechloride, heated while stirring until the methylene chloride hasevaporated and then further heated until 240° C. is reached. As soon asthe mixture has gelled, it is cooled, comminuted and finely ground in acolloid mill. One thus obtains a base grease which is to be assigned tothe penetration class 3 according to German Industrial Standard 51818.

To the so produced base grease are then added 2.5 wt.% of a mixture ofgraphite and molybdenum disulphide and 0.5% of a commercially availableoil-soluble anti-oxidant.

The so obtained lubricating grease is tested in the SRV apparatus. Theresults are given in test sheet 7922 accompanying as FIG. 2. One can seethat, in the case of a loading of 400 Newton and 80° C., after one and ahalf hours running period, a friction value between 0.093 and 0.110μ isachieved. The diameter of the abrasion ball amounts to 0.95 mm. Theprofile diagram of the surface of the frictional point shows a very goodstraight-lined course.

The experiment is repeated with the same base grease but withoutadditives. The SRV test sheet 7650 given in FIG. 3 shows the results.According to this, in the case of a loading of 300 Newton and 50° C.,after 2 hours test period the lubricating action has failed and anerosion has occurred. The diameter of the abrasion ball amounted to 1.35mm., the profile depth on the frictional point 12.0 μm. in comparisonwith 1.0 μm. in the case of the product with additives. The profilogramshows excessive wear up to erosion.

EXAMPLE 2

One proceeded as described in Example 1 but, instead of a saturatedmonofatty amine with 20 to 22 C-atoms, there was used an equivalentamount of simple unsaturated C18-alkenylamine (oleylamine). As additive,there was added an oil-soluble additive according to published FederalRepublic of Germany Patent Application No. 19 54 452, which contained Pband Mo dialkylthiophosphate, a metal-free sulphur-phosphorus compoundand an epoxide of an ester of an unsaturated fatty acid with an alkanol.

FIG. 4 of the drawing shows the results of the SRV test in the form ofthe test sheet 8286. One can see therefrom that, in the case of aloading of 300 Newton, there is achieved a friction value of 0.030μ andthe diameter of the abrasion ball only amounted to 0.65 mm. The runningin time up to the achievement of the low friction value is short, theprofilogram shows a very good course.

EXAMPLE 3

The process of Example 2 is repeated but, instead of the oil-solubleadditives, there are used the additives of Example 1 in the there-givenamount. The results of the test on the SRV apparatus are shown in FIG. 5of the drawing in the form of test sheet 8245. The minimal frictionvalue amounts to 0.085μ, the diameter of the abrasion ball to 0.50 mm.at 300 Newton loading.

EXAMPLE 4

A lubricating grease was produced as described in Example 1 but, insteadof 800 g. isocyanate solution, there were used 1200 g. the instead of0.5% anti-oxidant 3%.

The so obtained lubricating grease was investigated on a drive shafttest bench. For this purpose, the coupling was heated to 75° C.surrounding temperature and then loaded at 1200 rotations, 8° bendingangle and 320 Nm. In the case of an evaluation scale of 1 to 6, in which1 represents the best and 6 the worst value, with the best series greasebased on lithium soap obtainable commercially there was obtained anevaluation of 4.3±1 and an external temperature of 103±10° C., whichcorresponds to a coupling internal temperature of 105° to 130° C.

With the grease according to the invention, under the same conditions,there was achieved an evaluation of 3.0±1 and an external temperature of95±10° C. However, solely due to the temperature reduction, in the caseof the lubricating grease according to the invention there can beexpected a doubling of the period of life of the coupling quite apartfrom the fact that the series grease works on the limit of its prolongedtemperature stability, whereas the grease according to the inventionlies far below such a limiting value and thus offers a large safetyreserve.

We claim:
 1. In a lubricating grease composition of the type whereinmineral or synthetic oil is thickened to the properties of a lubricatinggrease with a polyurea compound as thickening agent, the improvementwherein, said polyurea compound comprises the reaction product of anisocyanate with at least 3 isocyanate groups in the molecule with along-chained straight-chained or branched aliphatic monoamine.
 2. Thelubricating grease cmposition of claim 1, containing 3 to 45 wt.% ofpolyurea, referred to the base oil.
 3. The lubricating greasecomposition of claim 1 or 2, wherein the polyurea is based upontriphenylmethane triisocyanate.
 4. The lubricating grease composition ofclaim 1 wherein the polyurea comprises an alkenylamine with 18 C-atomsas amine component.
 5. The lubricating grease composition of claim 1wherein the polyurea comprises a saturated C20 to C22 alkylamine asamine component.
 6. The lubricating grease composition of claim 5,further comprising oil-soluble high pressure and/or anti-wear additives.7. The lubricating grease composition of claim 6, containing 3 to 20wt.% of said additives.
 8. The lubricating grease composition of claim5, further comprising non-oil-soluble high pressure and/or anti-wearadditives.
 9. The lubricating grease composition of claim 8, comprisinggraphite and/or a lubricating-active metal sulphide as said highpressure or anti-wear additive.
 10. The lubricating grease compositionof claim 9, comprising 0.5 to 10 wt.% of said additives.
 11. Thelubricating grease composition of claim 1 further comprising 2 to 6 wt.%of non-oil-soluble additives or 3 to 12 wt.% of oil-soluble additives.12. In a process for the production of a lubricating grease compositionof the type comprising mineral or synthetic base oil thickened withpolyurea, the steps comprisingdissolving a long-chained aliphatic amineor a mixture of such amines in the base oil, adding thereto isocyanatewith at least 3 isocyanate groups in the molecule, heating the mixtureto a temperature of at least 160° C. to bring about gelling, andmechanically finely comminuting the gelled product.
 13. The process ofclaim 12, wherein 1/2 to 4 equivalents of isocyanate groups per aminegroup are added.
 14. The process of claim 12, wherein the amine isoleylamine or a saturated alkylamine or alkylamine mixture with 20 to 22C-atoms.
 15. The process of claim 12 wherein the isocyanate istriphenylmethane triisocyanate.